As detection apparatuses which measure a meteorological phenomenon, such as precipitation, weather radar apparatuses are known (e.g., see Patent Document 1). The weather radar apparatus disclosed in Patent Document 1 acquires a horizontally polarized wave reception signal and a vertically polarized wave reception signal from reflection waves caused by emitting a horizontally polarized wave and a vertically polarized wave, respectively. The weather radar apparatus further calculates a horizontal radar reflection factor Zh, a propagation phase difference change rate Kdp, etc. based on the horizontally polarized wave reception signal and the vertically polarized wave reception signal.
The weather radar apparatus obtains a three-dimensional distribution of a precipitation intensity in an observation range based on the horizontal radar reflection factor Zh, the propagation phase difference change rate Kdp, etc. The weather radar apparatus measures the precipitation intensity for each given space. The given space is defined as a three-dimensional space having a given length (depth) in horizontal directions and a given height in vertical directions.
The weather radar apparatus further stores blocking map data as data specifying an area where a radar beam emitted by the weather radar apparatus is at least partially blocked. For every mesh segment formed for each altitude in the observation range, the weather radar apparatus specifies whether the mesh segment indicates an area where at least a part of the radar beam is blocked by using the blocking map data. Then, the weather radar apparatus calculates a rainfall intensity by using the blocking map data for each area of the observation range.